1. Technical Field
The present invention relates to a foamed body molding system that molds a foamed tube used as an elastic roller of a fixing device provided in an electro-photographic image forming apparatus such as a copier, a printer, a facsimile machine, a multi-functional machine including multiple functions of these devices, etc.
2. Related Art
A known fixing device used in an image forming apparatus sometimes employs a thin fixing belt typically constructed of a metallic substrate and an elastic rubber layer overlying the metallic substrate.
Since it has a low heat capacity, the energy needed to heat the thin fixing belt to a prescribed temperature can be significantly reduced. As an example, a warm-up time (i.e., the time period needed to raise temperature from a room temperature the thin fixing belt to a prescribed printing temperature) can be shortened. As another example, a first printing time (i.e., the time from when a printing request is received to when a printed sheet is generated in a printing process) can be reduced as well.
In a fixing device employing the above-described fixing belt, a pressing roller is opposed to and contacted against the fixing belt to form a nip between the pressing roller and the fixing belt and transmit rotating power to the fixing belt at the same time. Conventionally, the pressing roller of the fixing device has an elastic layer composed of soft sponge made of foamed silicone rubber overlying a rotational shaft thereof. With the soft sponge of the foamed silicone rubber, since the warm-up time can be shortened while obtaining sufficient contact (i.e., a nip width) in the fixing device as well, a toner image can be appropriately fixed on the recording medium by the fixing device.
However, although the warm-up time can be shortened, the soft sponge of the foamed silicone rubber is quickly destroyed by external forces applied to the soft sponge elastic layer.
To solve this problem, a roller having a foamed body elastic insulating layer made of water-blown foamed silicone rubber having continuous air bubbles has been proposed. The foamed body elastic insulating layer is prepared by using a composition of emulsified silicone rubber using water regarded as a dispersant (hereinafter sometimes referred to as emulsion).
With the water-blown foamed silicone rubber, since air bubbles become finer and continuous, and accordingly the diameter of the roller does not thermally increase and the air bubbles are not broken, the roller can maintain a prescribed diameter and hardness thereof at the same time as well (even when it is heated during the molding process). As a result, the roller can obtain a prescribed degree of high durability.
However, even such a roller is not sufficiently durable and is to be further improved when actually employed in a fixing device of an image forming apparatus.